[PATCH net-next, v7 2/2] selftests/net: Add selftest for IPv4 RTM_GETMULTICAST support

[Yuyang Huang <yuyanghuang@google.com>]

This change introduces a new selftest case to verify the functionality
of dumping IPv4 multicast addresses using the RTM_GETMULTICAST netlink
message. The test utilizes the ynl library to interact with the
netlink interface and validate that the kernel correctly reports the
joined IPv4 multicast addresses.

To run the test, execute the following command:

$ vng -v --user root --cpus 16 -- \
    make -C tools/testing/selftests TARGETS=net \
    TEST_PROGS=rtnetlink.py TEST_GEN_PROGS="" run_tests

Cc: Maciej Żenczykowski <maze@google.com>
Cc: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Yuyang Huang <yuyanghuang@google.com>
---

Changelog since v6:
- Move `getmaddrs` definition to rt_addr.yaml.

 Documentation/netlink/specs/rt_addr.yaml  | 23 +++++++++++++++++
 tools/testing/selftests/net/Makefile      |  1 +
 tools/testing/selftests/net/lib/py/ynl.py |  4 +--
 tools/testing/selftests/net/rtnetlink.py  | 30 +++++++++++++++++++++++
 4 files changed, 56 insertions(+), 2 deletions(-)
 create mode 100755 tools/testing/selftests/net/rtnetlink.py

diff --git a/Documentation/netlink/specs/rt_addr.yaml b/Documentation/netlink/specs/rt_addr.yaml
index cbee1cedb177..5dd5469044c7 100644
--- a/Documentation/netlink/specs/rt_addr.yaml
+++ b/Documentation/netlink/specs/rt_addr.yaml
@@ -168,6 +168,29 @@ operations:
         reply:
           value: 20
           attributes: *ifaddr-all
+    -
+      name: getmaddrs
+      doc: Get / dump IPv4/IPv6 multicast addresses.
+      attribute-set: addr-attrs
+      fixed-header: ifaddrmsg
+      do:
+        request:
+          value: 58
+          attributes:
+            - ifa-family
+            - ifa-index
+        reply:
+          value: 58
+          attributes: &mcaddr-attrs
+            - ifa-multicast
+            - ifa-cacheinfo
+      dump:
+        request:
+          value: 58
+            - ifa-family
+        reply:
+          value: 58
+          attributes: *mcaddr-attrs
 
 mcast-groups:
   list:
diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index 73ee88d6b043..e2f03211f9b3 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -36,6 +36,7 @@ TEST_PROGS += cmsg_so_priority.sh
 TEST_PROGS += cmsg_time.sh cmsg_ipv6.sh
 TEST_PROGS += netns-name.sh
 TEST_PROGS += nl_netdev.py
+TEST_PROGS += rtnetlink.py
 TEST_PROGS += srv6_end_dt46_l3vpn_test.sh
 TEST_PROGS += srv6_end_dt4_l3vpn_test.sh
 TEST_PROGS += srv6_end_dt6_l3vpn_test.sh
diff --git a/tools/testing/selftests/net/lib/py/ynl.py b/tools/testing/selftests/net/lib/py/ynl.py
index ad1e36baee2a..7b1e29467e46 100644
--- a/tools/testing/selftests/net/lib/py/ynl.py
+++ b/tools/testing/selftests/net/lib/py/ynl.py
@@ -38,8 +38,8 @@ class EthtoolFamily(YnlFamily):
 
 
 class RtnlFamily(YnlFamily):
-    def __init__(self, recv_size=0):
-        super().__init__((SPEC_PATH / Path('rt_link.yaml')).as_posix(),
+    def __init__(self, recv_size=0, spec='rt_link.yaml'):
+        super().__init__((SPEC_PATH / Path(spec)).as_posix(),
                          schema='', recv_size=recv_size)
 
 
diff --git a/tools/testing/selftests/net/rtnetlink.py b/tools/testing/selftests/net/rtnetlink.py
new file mode 100755
index 000000000000..b12e12827219
--- /dev/null
+++ b/tools/testing/selftests/net/rtnetlink.py
@@ -0,0 +1,30 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+from lib.py import ksft_exit, ksft_run, ksft_ge, RtnlFamily
+import socket
+
+IPV4_ALL_HOSTS_MULTICAST = b'\xe0\x00\x00\x01'
+
+def dump_mcaddr_check(rtnl: RtnlFamily) -> None:
+    """
+    Verify that at least one interface has the IPv4 all-hosts multicast address.
+    At least the loopback interface should have this address.
+    """
+
+    addresses = rtnl.getmaddrs({"ifa-family": socket.AF_INET}, dump=True)
+
+    all_host_multicasts = [
+        addr for addr in addresses if addr['ifa-multicast'] == IPV4_ALL_HOSTS_MULTICAST
+    ]
+
+    ksft_ge(len(all_host_multicasts), 1,
+            "No interface found with the IPv4 all-hosts multicast address")
+
+def main() -> None:
+    rtnl = RtnlFamily(spec='rt_addr.yaml')
+    ksft_run([dump_mcaddr_check], args=(rtnl, ))
+    ksft_exit()
+
+if __name__ == "__main__":
+    main()
-- 
2.48.1.362.g079036d154-goog